This invention relates to sound systems and in particular to a new and improved compatible mono/stereo photographic sound system with data control, especially suited for use in motion picture theaters.
Stereophonic sound systems have been known for many years. British patent to Blumlein, No. 394,325 discloses most of the significant features and 2 channel systems have been used extensively since about 1958. A multi-channel sound system was used in the motion picture Fantasia. (U.S. Pat. No. 2,298,618) This system was extremely complex and expensive and has not been used since the 1939 production. In 1953, CinemaScope was introduced with four magnetic tracks striped on the motion picture film, with three of the sound channels positioned behind the screen at the left, center and right, with the fourth channel sometimes refered to as a surround track. This fourth channel fed a plurality of speakers positioned at the sides and back of the theater with all speakers connected together. The fourth track was switched on to produce a dramatic effect when desired. A later variation known as "Todd-AO" utilized 6 magnetic tracks on the film, with 5' speakers behind the screen and the sixth track used to drive the speakers at the sides and back of the theater. None of these configurations have been particularly satisfactory because of their added cost and technical difficulties both in making the special prints and maintaining the complex theater systems, compared to the standard photographic single channel soundtrack.
In order to maximize the use of 35 mm prints, magnetically striped and recorded for 4 channel stereophonic sound, the monophonic photographic sound track has been added, thereby making a compatible print. But as aforesaid, this process is seldom used because of its cost and technical difficulties. In recent years there has been a renewed interest in multi-channel stereophonic sound for motion pictures and television. Since the photographic soundtrack is applied and processed simultaneously with the picture, there are obvious advantages to be had by confining film sound to this format. Throughout the history of sound on film covering the last 50 years, many photographic formats have been used, covering the sound itself and means of controlling it. Both single ended and push-pull systems have been used. Since about 1938, all films released for normal threatrical exhibition have had their soundtrack made to conform to the "Academy Curve". This was fully described by the Motion Picture Research Council in their publication entitled, "Standard Electrical Characteristics for Theater Sound Systems", dated April 20th, 1948. This curve was derived empirically to give the best compromise between signal to noise ratio, dynamic range and frequency response. It is shown as FIG. 1 hereof. It will be appreciated that this curve is a far cry from the modern ideal of a wide range Hi-Fi system. Furthermore, in order to obtan satisfactory sound in the theaters, the recordings are made with considerable upper mid-range and high frequency pre-emphasis.
Despite numerous attempts to circumvent the Academy Curve, no commercial system exists. It must be understood that of the 85,000 theaters situated in the western world, less than 10% are able to reproduce anything other than the Academy Curve. A key part of this invention is the inclusion of an Academy track situated in such a way that whenever a film recorded in accordance with this invention is placed upon a standard Academy reproducer, it will be virtually indistinguishable from the same material recorded with a standard optical recorder. Simultaneously the soundtrack described in this invention contains a minimum of four additional soundtracks for stereophonic sound plus extra tracks for data, automatic switching and guidance. By using a suitable data system such as the SMPTE time code, useful information and commands can be stored on a per frame basis.